1. Field of the Invention
This invention relates to an improved head shell for pickup arms and a method of making same.
2. Discussion of the Prior Art
Conventionally, as shown in FIG. 1, head shells comprise a horizontal part 1 for mounting a cartridge and a vertical part 2 formed at the back end of horizontal part 1 for mounting a connector 3. Connector 3 is affixed onto vertical part 2 by means of caulking, screwing, or adhesion. The cross-sectional forms of horizontal part 1 are roughly as shown in FIGS. 2(A), 2(B) and 2(C). As for the material and forming methods, the head shells are made of light alloys of aluminum, magnesium, ceramic, etc. by means of forging, die casting, or plastic molding.
In general, the required characteristics for this type of head shell are lightness, adequate bending and torsional strengths, large dampening factor, etc. In the case of conventional head shells, the lightness requirement is more or less satisfied; however, the bending and torsional strengths have been inadequate. Consequently, as shown at r in the frequency response graph of FIG. 3, partial resonance occurs resulting in an inferior sound quality. This is attributable to the inadequate strength of the head shell in view of the connector 3.
Some head shells made of carbon fiber has been introduced to overcome aforementioned defects. However, one of these shells is made by plastic molding mixed with briefly cut carbon fiber chop, and another is made by using long carbon fiber. In this kind of shell using long carbon fiber, cross-section of the shell is seen in FIG. 2(C), because that of FIG. 2(A) or 2(B) is difficult to form. In the former case, mechanical strength, especially bending elasticity is poor because of briefly cut carbon fiber. In the latter case, mechanical strength is poor because of the hole for mounting a connector in the vertical part 2.